It's probably Microsoft trying to validate your OS because of your new hard drive.
You can go to microsoft.com and click on the Security & Updates tab -- then click Update -- Microsoft will do a quick scan and give you various updates, one of which will probably be their validation tool. After you run the updates, if all is in order, you will no longer receive those notifications.
If after you update, you get a notice that your Windows install may not be genuine, just call the phone number they give you to get it validated -- once you inform Microsoft that you had a hard drive crash and you reinstalled the original OS that came with your computer (using your official IBM/Lenovo restore disks) they will approve your installation and you will be good to go.
Best case -- you complete Microsoft's Validation and nothing further needed.
Second best -- you call Microsoft, which will only take a few minutes of your time, and then you will be done with it.
Also, you can download Microsoft Security Essentials, free from microsoft.com -- everyone has their favorite security suites, and I don't care for Norton -- it always gave me issues and seemed to slow down my machines -- I have McAfee Security Suite provided by my DSL provider -- it has always worked for me, and in the past I would have purchased it if it were not given to me free. But recently I have used Microsoft Security Essentials for family members or friends for whom I have helped set up their machines -- it seems to work very well -- I read good reports about it -- and it does not slow down their machines --
and it's free -- If I didn't have McAfee provided to me, I would definitely use Microsoft Security Essentials.
Check around -- others may have better info -- but a google search shows good reviews for Microsoft Security Essentials, and my friends and family are happy with their installations.
EDIT:
can l delete it without leaving something behind to slow up my computer
Norton can be hard to delete. There is a very good program I have used for several years called Revo Uninstaller. You can download it free at download.com -- It uses very little resources and in all the times I have used it (on lots of different machines and lots of different programs) it has never caused a problem, and has always completely deleted whatever I needed gone.